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    <title>Document</title>
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<body>
<script>
    setTimeout(function(){
        console.log(1)
    })
    new Promise(function (resolve,reject){
        console.log(2)
        resolve()
    }).then(function (){
        console.log(3)
    }).then(function (){
        console.log(4)
    })
    console.log(5)
    //执行结果：25341
    //1.限制性所有同步任务
    //2.再执行微任务(then)
    //3.在执行宏任务(setTimeout)

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